"We still have massive amounts of rain hitting Ohio, Michigan, Indiana, Illinois and Missouri. Those are the states already behind in planting," Pierce says.

On Thursday, the December CBOT corn contract set a new all-time high of $6.46 per bushel.

Don Roose, U.S. Commodities, says the Dec. corn contract, representing new crop corn, will be the focus from here on out.

"July will die in the middle of the month of July, while this market will continue deep into the summer," Roose says. I think for Dec. corn the upside price objective, with rationing, is closer to $7.00," Roose says. "Especially if something goes wrong with the growing season."

Roose says corn remains the floor leader because the U.S. is struggling to keep the 2008/09 ending stocks above the pipeline minimum of 650 million bushels.

"The use of corn for biofuels, strong export demand, and feed usage, is drawing corn stocks down to very tight levels. All three areas are very strong in usage numbers," Roose says.

Last year's record-high corn acres pushed up soybean prices, in an attempt to lure producers to plant more soybeans.

However, all of this happened before the wet spring planting weather set in. Now, with the wet weather market cutting back some corn acres, the market is trying to buy back some corn acres.

Meanwhile, traders say history shows delayed planting can result in fewer corn acres.

In 1995, when it was wet, the U.S. lost 3.0 million corn acres from March to June.

"In addition, last year's delayed planting resulted in lower than trendline yields. And last year's planting pace was faster than this year's is going," Roose says. All of these points are supportive for corn prices.

For soybeans, it's hard to capture the lead role on the trade floor when a number of bearish factors are lining up such as a large South American crop hitting the export market, and possibly more corn acres being switched to soybeans.

For wheat, big prices earlier this year brought big production around the world, so supplies are going to build significantly this year.

"You have two different things going on. For corn it's weather and questions about the ethanol future that is driving that market, and for soybeans the Argentine strike talks. There is no real leader," Hollander says.